Anurans typically rely on acoustic communication for pair formation in the breeding season. However, acoustic signals are regularly emitted in the forests during the non-breeding season in Hyla japonica. In this study, we characterized the calls of H. japonica in the breeding and non-breeding seasons through a year-round acoustic survey and individual recordings of H. japonica. Acoustic signals were recorded from rice paddies and nearby forest in Paju, South Korea from the beginning of the breeding season to the week after the last call was heard. In non-breeding season, calls were produced by significantly smaller number of H. japonica males, and they called high up in the trees.  When compared with individuals recorded in the breeding season, difference in dynamic properties (gross temporal properties) were shown. However, there was no significant difference in dominant frequency. These results suggest possibility of conspecific male interactions in non-breeding season. Possible explanation of energetically costly calls produced in non-breeding season needs further exploration and experiment.